This is a proposal to investigate how the interactions between central control neurones and peripherally based cells enmeshed in a nerve plexus are able to encode specific behaviors. As a model system we are investigating the control of locomotion in the polyclad flatworm, Notoplana acticola. Central control neurones are in a small brain which is amenable to intracellular electrophysiology. The brain cells themselves are unusual in that they are multipolar like those of vertebrates, unlike unipolar cells of invertebrates. The plexus is in close association with the brain and it is possible to dissect it out and record or stimulate at known positions. The role of individual cells and their branches in the control of behavior will be assessed through conventional, intracellular, electrophysiological techniques, along with intracellular injection of fluorescent Lucifer yellow and/or electron-opaque horseradish peroxidase (HRP) stains. Ablation of entire Lucifer-filled cells or specific branches by micro laser irradiation will allow assessment of their contributions to the normal workings of the system. Electron microscopical examination of HRP-filled cells will provide information concerning synaptic interactions between brain cells, as well as between the central and peripheral nervous system. Additionally it will help confirm or deny the possible vertebrate-like characteristics of the neurones. Initiation of locomotion in this system requires arousal. Vibration is an effective arousal mechanism. Vibration-sensitive cells in the brain (already identified) will be studied using standard intracellular methods and their impact on other control neurones determined.